(a) Technical Field
The present invention relates to a method of manufacturing Ni-doped TiO2 (titanate) nanotube-shaped powder and a method of manufacturing a sheet film for a high-pressure hydrogen tank for a fuel cell vehicle using the same. More particularly, the present invention relates to a method of manufacturing Ni-doped TiO2 nanotube-shaped powder capable of storing a greater amount of hydrogen, and a method of manufacturing a sheet film to be inserted into a high-pressure hydrogen tank for a fuel cell vehicle by mixing the Ni-doped TiO2 nanotube-shaped powder with a binder and compressing the mixture.
(b) Background Art
In the recent years, the international situation concerning energy has undergone a sudden change. Especially, as energy problems are associated with environmental problems and strengthened, international environmental regulations including greenhouse gas emission reduction becomes more stringent from the recognition that the structure of energy consumption based on fossil fuels generally causes environmental contamination including global warming.
With the rapid expansion of alternative energy development over the strengthening of environmental regulations and the high oil prices, the energy industry has broken from its smokestack-industry image and created international high-technology competition.
Accordingly, the development of a hybrid material using hydrogen energy for the purpose of developing a material capable of improving energy efficiency and providing ultra-clean energy is an essential task affecting the very existence of the nation and an essential selection for the development of energy resource technology.
Although extensive research aimed at storing hydrogen which is the next generation energy source has continued to progress throughout the world, the exact reaction mechanism of hydrogen storage has not yet been established.
Moreover, the difficulties in reducing the weight of material and realizing practical reaction temperature and pressure and the problem of safety have not been solved.
Meanwhile, although titanate nanotubes were synthesized in 1998, since the results of the study on structural characteristics and phase were not given at that time, the titanate nanotubes were called TiO2 nanotubes.
Recently, the TiO2 nanotubes are prepared by forming a template using porous alumina (Al2O3) and synthesizing TiO2 in its pores.
Such a method is called a template method, in which aluminas or organic materials formed by alumina are used as the template. With the template method, it is possible to manufacture nanotubes having a relatively uniform direction compared with other methods.
However, the template method has some drawbacks in that the diameter of the nanotubes is relatively large, a high cost is required for removing the templates, and impurities remain.
To overcome such drawbacks, a method of synthesizing TiO2 of anatase phase by coating TiF4 on nanochannels of a porous alumina membrane has been proposed. That is, oversaturated Ti is coated on the inside surface of alumina using a characteristic in which TiF4 in an acidic state is bonded to a hydroxyl group (—OH).
Since such a method does not require a heat treatment, the shape is not deformed; however, the process is complicated.
The first method which does not use the template is a method of manufacturing titanate nanotubes by doping a small amount of SiO2, instead of using pure TiO2 powder, to form TiO2 in the form of nanotubes and removing the SiO2.
According to the above method, a mixed solution of TiO2 and SiO2 in the ratio of 8:2 is mixed with ethanol and an HCl solution to form gel in an incubator, the thus formed gel is heat treated to form anatase powder, and the powder is immersed in an alkali solution and washed, thus preparing titanate nanotubes.
However, although it is possible to prepare nanotubes having a length of about 100 nm and a diameter of about 8 nm by the above method, it has also some drawbacks in that the SiO2 should be removed and the activity of a photocatalyst is reduced due to the doped SiO2.
Especially, a strategic study has been carried out by DOE of USA since a hydrogen storage method using carbon nanotubes (CNT) was attempted by Bethune et al. of IBM Corp., USA in 1997; however, they have been faced with limitations and a discussion of whether or not to continue the study has continued.
The CNT can be manufactured by various methods such as arc-discharge, laser vaporization, plasma enhanced CVD, thermal chemical vapor deposition, and the like; however, it has some drawbacks in that its reproductivity is poor according to the methods, the hydrogen stored in the CNT is spontaneously desorbed due to unstable physical absorption between the carbon surface and hydrogen molecules at room temperature and at high temperature, and it requires an extremely low temperature condition since the hydrogen is physically absorbed.
However, in the event that the titanate nanotubes are annealed under vacuum or under a hydrogen atmosphere, n-type rutile or hypostoichiometric phase TinO2n−1 is formed.
Such phases are used as very important catalysts and, especially, it is reported that the diffusion rate of hydrogen through c-axis is greater than the hydrogen diffusion coefficient D=2*10−8 cm2S−1 at 400° C. of Ti isotope.
Moreover, in case of the titanate nanotubes, the physical absorption which is the most significant weak point of the CNT is improved and thus the hydrogen storage is available physically and chemically. Accordingly, the titanate nanotubes can be developed as a promising alternative material for storing hydrogen and have advantages in that the manufacturing cost is low, mass production is available, and thus their industrial application is high.
Generally, in order to store much more hydrogen, a greater number of sites for storing hydrogen, an increase in surface area capable of reacting with a greater amount of hydrogen at a time, and a high reactivity with hydrogen should be taken into consideration.
Accordingly, the possibility of the titanate nanotubes as a good hydrogen storage material is expected due to ultra-long nanochannels capable of storing hydrogen molecules and a high specific surface area.
Meanwhile, a research on a metal hydride high pressure hydrogen storage tank, into which Ti—Cr—Mn is inserted, capable of storing hydrogen of about 2.2 wt % at 35 MPa has been carried out by Toyota Japan.
However, Ti—Cr—Mn is a typical AB2 type metal hydride and has some drawbacks in that its reproductivity is poor in preparing powder, it is difficult to stably supply a large amount of alloy of stable quality, segregation and impurities may be incorporated in dissolving the alloy, an initial activation temperature is high, and the storage amount is sensitively changed by the Cr content.
Moreover, in the event that the metal hydride powder is compressed and inserted into the tank, a hydrogen storage reaction hardly occurs on the surface of the compressed powder to reduce the actual amount of hydrogen stored, and it causes a safety problem since it requires a very high pressure for the operation.
The information disclosed in this Background section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.